Pathogenic Bacteriology

1. Pathogenic Bacteriology Introduction

2. What the class will cover: • Clinically significant bacteria • Morphological characteristics • Biochemical characteristics • Signs and symptoms they cause in the host they are infecting • Virulence factors • Pathophysiology of infection

3. Clinically significant bacteria • Propensity to cause disease, i.e., how likely are they to cause disease • Opportunistic pathogens – only cause disease in immunocompromised hosts • AIDs patients • Transplant patients on immunosupressive drugs • Cancer patients undergoing chemotherapy • Patients who are already ill • Opportunistic pathogens are often organisms that are typically normal flora. • Staphylococcus epidermidis and intravenous catheters • Given the right circumstances any organism can be invasive and lethal

4. Clinically significant bacteria • Frank pathogens are always associated with disease • Neisseria gonorrhoeae • Shigella species • Facultative pathogens fall between the two extremes (opportunistic and frank) and the majority of organisms that cause disease fall into this group • Staphylococcus aureus • E. coli

5. Clinically significant bacteria • Various factors involved in the host-parasite interaction determine whether an organism will cause disease in the host: • Virulence factors of the bacteria including: • Capsules • Pili • IgA protease production • Iron capturing ability • Production of coagulase • Production of toxins • Ability to survive inside phagocytic cells

6. Clinically significant bacteria • Degree of resistance of the host • Age • Gender • Physical health • Mental health • Antibiotic therapy that disrupts the normal balance between the host and normal flora • From the organisms point of view, the most successful pathogen is NOT the one that inflicts the most extensive damage on the host, but rather the one that can establish a balanced pathogenicity with the host. Parasites that kill the host will eventually lead to their own extinction.

7. Clinically significant bacteria • Severe human infections - often from zoonotic organisms • No balanced pathogenicity • Humans irrelevant for organism’s survival - Humans simply serve as accidental hosts. • Bubonic plaque • Anthrax • Leptospirosis • Based on your knowledge of normal flora and the propensity of organisms to cause disease, you may be asked to determine the likelihood that a clinical isolate is causing disease. Things to consider are: • Site from which the organism was isolated (E. coli in G.I. tract versus the urinary tract) • Relative numbers of organism isolated • Age of patient

8. What the class will cover: • Media • Content • Usage • Appropriate positive and negative controls • What information can be gained by using the media • How to read results on the media

9. What the class will cover: • What is the difference between pathogenicity and virulence? • Pathogenicity is the potential to cause disease and is applied to groups or species of organisms • Virulence is the degree of pathogenicity within a group or species and is measurable by the LD50 or the ID50.

10. LD50